Broken Mount For LA724

[Verticaltrx]

We're dealing with a tractor here, not a china cabinet after all. I doubt that moving it with the bucket bottom flat on the ground would put enough twisting torque into the mounting brackets to break the way they did. If anything, I think they should have broken out of the engine block since that is only bolt threads into cast iron.

From what I've seen of broken Kubota parts on TBN lately, I'm thinking they have a potential problem with steel quality in their attachments. The broken backhoe booms and now the loader bracket make me think there's more to this than just use or abuse. Steel shouldn't break like that, without bending first.

Thank God they aren't building bridges.

Sean

I don't see any abuse in this case either, nor do I think that the OP should have spent the extra money for a 'real' TLB. As far as I'm concerned even the standard Kubota tractors are what I would call commercial grade. Compare their loader and especially backhoe design with other compact tractor makes and it will reinforce this.

Now I'm speaking about the B-series here, because that's the only one that I have directly knowledge/use of. But the B26 is 90% a B2630, with a upgraded loader and backhoe (and third hyd. pump for BH swing). The subframe on the B26 is a little bit heavier, but is essentially the same design as that on the larger B-series. The main difference is that it is one entire weldment on the B26 vs. being bolted together on the standard B-series. The new BH77 is very similar to the BT820, except it has a slightly shorter boom/dipper, and less breakout force. The BH77 actually has more dipper stick force than the BT820 however. The TL500 loader is a good bit more substantial than the LA403 or LA504, but is has to be because of the greater lift capacity.

My point on all this is that the Kubota TLBs really do share a lot in common with the non-industrial tractors. They use some upgraded parts and weldments here and there, but otherwise they just combined parts, features and attachments from different models to make a tractor more desirable to the commercial contractor. Would I rather have a B26 over my B3200, probably not. Would I like to get a B26 in addition to my B3200 someday, definitely. The B26 can't do what my B3200 does, nor could my B3200 do the job of a B26 nearly as efficiently.

Now, the bigger issue here is what appears to be the lack of good materials and/or Quality Control. I may get bashed for this, but I think it has to do with the typical American spirit of buy materials as cheap as you can and build it as quick as you can to turn a good profit. Notice that almost all of the catastrophic metal failures that we read about in the Kubota forum have to do with either loaders or backhoes. Is it a coincidence that they are made in the USA, while the rest of the tractor comes directly from Japan? I can say without a doubt the welds on my LA504 loader are not nearly as nice as those on the tractor itself. I think it's time for Kubota Corporation Japan to have a talk with their American counterparts.

 

[PapaPerk]

The material is cast steel that is weldable similar to regular low carbon steel.

Hmmmm interesting. Must be ductile iron. Based on the photo you attached I'm guessing there was a defect (stress concentration) in the casting. That's very unfortunate.

Also the bracket cross section looks a bit undersized for this application. I'm not crazy about those "pockets" in the bracket arm. Not sure why those are there... maybe something to do with the casting process. But more likely an effort to save material or weight.... or dollars.

Kubota should certainly be informed of this issue. Sitting here in my arm chair, I believe it maybe a design problem with the brackets. 500 hours is not much for a tractor of this caliber. At 6000 to 7000 lbs your tractor is capable of producing some serious loading on all it's components.... an owner shouldn't be expected to baby a machine. Of course abuse is another story.

My L3830 has brackets that are weldments.... cut and bent metal plate that is welded together. I feel this design and manufacturing method is much more durable for the loader application. Especially when trying to maintain quality control that closely matches design intentions.

 

[PapaPerk]

Do you remember the John Deere trade-in thread with the 2520? His tractor was well taken care of, but I'm afraid he has nothing to compare to the care kcender takes of his equipment. I know him, and I can tell you one thing for sure, if it was abuse, which I'm not convinced it was, it was purely accidental.

We're dealing with a tractor here, not a china cabinet after all. I doubt that moving it with the bucket bottom flat on the ground would put enough twisting torque into the mounting brackets to break the way they did. If anything, I think they should have broken out of the engine block since that is only bolt threads into cast iron.

From what I've seen of broken Kubota parts on TBN lately, I'm thinking they have a potential problem with steel quality in their attachments. The broken backhoe booms and now the loader bracket make me think there's more to this than just use or abuse. Steel shouldn't break like that, without bending first.

Thank God they aren't building bridges.

Sean

Do you have the link to the backhoe failure? I would like to study.

 

[Baby Grand]

<<<snip>>>
Hmmmm interesting. Must be ductile iron. Based on the photo you attached I'm guessing there was a defect (stress concentration) in the casting. That's very unfortunate.

Also the bracket cross section looks a bit undersized for this application. I'm not crazy about those "pockets" in the bracket arm. Not sure why those are there... maybe something to do with the casting process. But more likely an effort to save material or weight.... or dollars.
<<<snip>>>


.

As was mentioned previously, that cast upright was not designed to take large side loads- it was designed to be loaded fore 'n aft. Take a yardstick as an example - it can support a lot more weight on it's narrow edge than on its broad edge.

The pockets in the casting are there for the same reason that an I-Beam isn't a solid, rectangular section: the added material would reduce the strength to weight ratio. It also helps the casting to cool evenly after it's poured; without deforming. Kubota does a pretty good job of wringing weight out of their products without going overboard. I don't think a casting defect is indicated.

It looks to me like the loader had a side load in excess of what it was designed for. Surprisingly, the loader manual makes no warnings about side loading the attachment that I could find. Don't know if the backhoe manual says anything about that as I don't have one ... yet.

I guess the take away from all this is to lift the bucket before moving the tractor with the hoe. My condolences to the OP for having to find this out the way he did. Sounds like he's a more than competent weldor who can set it right if the dealership won't. It's nice to have that skill as an option.

-Jim

 

[PapaPerk]

As was mentioned previously, that cast upright was not designed to take large side loads- it was designed to be loaded fore 'n aft. Take a yardstick as an example - it can support a lot more weight on it's narrow edge than on its broad edge.

The pockets in the casting are there for the same reason that an I-Beam isn't a solid, rectangular section: the added material would reduce the strength to weight ratio. It also helps the casting to cool evenly after it's poured; without deforming. Kubota does a pretty good job of wringing weight out of their products without going overboard. I don't think a casting defect is indicated.

It looks to me like the loader had a side load in excess of what it was designed for. Surprisingly, the loader manual makes no warnings about side loading the attachment that I could find. Don't know if the backhoe manual says anything about that as I don't have one ... yet.

I guess the take away from all this is to lift the bucket before moving the tractor with the hoe. My condolences to the OP for having to find this out the way he did. Sounds like he's a more than competent weldor who can set it right if the dealership won't. It's nice to have that skill as an option.

-Jim

Can you explain to me how moving the tractor around with the backhoe produces side loading at the brackets?

There's no way the backhoe can drag the tractor sideways. The tractor will rotate (pivot) about the bucket that is on the ground. This movement will produce a force along the L (length) direction of the tractor... one bracket will have a force towards the rear and one towards the front. Side loading will be very minimal.

Short of pushing hard on the loader brackets from the side, I see no way to side load the brackets when operating the tractor. Hence no need for a safety warning to not side load them from the manufacture.

 

[PapaPerk]

Most likely the right hand loader bracket failed AFTER the left hand loader bracket broke completely through.

 

[teg]

Do you have the link to the backhoe failure? I would like to study.

http://www.tractorbynet.com/forums/kubota-owning-operating/181076-broken-kubota-backhoe.html

Careful, the OP had started the thread and the thread was brought back to life with another poster at post number 23.

 

[beppington]

Can you explain to me how moving the tractor around with the backhoe produces side loading at the brackets?

There's no way the backhoe can drag the tractor sideways. The tractor will rotate (pivot) about the bucket that is on the ground. This movement will produce a force along the L (length) direction of the tractor... one bracket will have a force towards the rear and one towards the front. Side loading will be very minimal.

Short of pushing hard on the loader brackets from the side, I see no way to side load the brackets when operating the tractor. Hence no need for a safety warning to not side load them from the manufacture.

What if he had the loader in "float", so the weight was actually on the front wheels? When he moves the rear of the tractor to the left (when sitting on the BH seat), the tractor would pivot on the front wheels & the loader bucket would slide to the right (when sitting on the BH seat). The loader bucket could have caught on something when it was sliding, & using the BH to force the front bucket past the obstacle could've put some serious side force on the loader frame.

 

[PapaPerk]

What if he had the loader in "float", so the weight was actually on the front wheels? When he moves the rear of the tractor to the left (when sitting on the BH seat), the tractor would pivot on the front wheels & the loader bucket would slide to the right (when sitting on the BH seat). The loader bucket could have caught on something when it was sliding, & using the BH to force the front bucket past the obstacle could've put some serious side force on the loader frame.

Yes in that case it would apply a force AND moment to the loader attachment brackets. Especially if the loader was against a tree stump or large rock.

 

[Grateful11]

Hmmmm interesting. Must be ductile iron. Based on the photo you attached I'm guessing there was a defect (stress concentration) in the casting. That's very unfortunate.

Also the bracket cross section looks a bit undersized for this application. I'm not crazy about those "pockets" in the bracket arm. Not sure why those are there... maybe something to do with the casting process. But more likely an effort to save material or weight.... or dollars.

Kubota should certainly be informed of this issue. Sitting here in my arm chair, I believe it maybe a design problem with the brackets. 500 hours is not much for a tractor of this caliber. At 6000 to 7000 lbs your tractor is capable of producing some serious loading on all it's components.... an owner shouldn't be expected to baby a machine. Of course abuse is another story.

My L3830 has brackets that are weldments.... cut and bent metal plate that is welded together. I feel this design and manufacturing method is much more durable for the loader application. Especially when trying to maintain quality control that closely matches design intentions.

The close up of the break is too blurred to tell if it's ductile iron or cast steel. I'm leaning towards cast steel as the reflection off the break is quite shiny.